The present invention relates to an optical-disk recording medium in which main data is recorded in the form of a combination of pits and lands formed on one side of a substrate, a reflective layer and cover layer are stacked over the substrate side where the pits and lands are formed, sub data is recorded in the form of marks formed by irradiating laser light having a writing power to the reflective layer and the output level of a reading signal will be raised at the portions where the marks are formed, a playing apparatus and method for the optical-disk recording medium and a recording apparatus and method for recording sub data to the optical-disk recording medium.
The optical disks used to record information include the ROM (read-only memory). The ROM disk is widely used as a package medium over the world because many replica substrates thereof can be produced in a short time by injection molding of plastics with a stamper having pits and lands formed thereon in advance. Of the ROM disks of this type, CD (Compact Disk) and DVD (Digital Versatile Disk), for example, are widely used as recording media to record content information such as music, video, etc.
Disks having illegally copied thereto data recorded in a ROM disk sold as a package medium, so-called counterfeit disks, have ever been produced and prejudicial to the interests of a person having the regular copyright for the data in the ROM disk.
Generally, the counterfeit disks are produced by forming a stamper by mastering on the basis of signals read from an authenticated disk and replicating optical disks by the stamper, or by copying signals read from the authenticated disk to recordable disks.
Various techniques for copy prevention have been proposed heretofore to prevent such counterfeit information-recording media from being produced by those having no due right. One of such techniques is to append, for example, unique identification information to each of disks. There can be built a system in which unique identification information is appended to each disk with this technique, and a disk player reads the identification information and sends it to an external server via a network. Even if such counterfeit disks have been produced and distributed, the external server will detect a large amount of the same identification information and the system can thus detect that the counterfeit disks have been so produced and distributed. Further, the system can also identify a counterfeit disk maker or distributor by identifying a disk player having sent the detected identification information to the external server.
Even identification information unique to each authenticated disk should be recorded not to easily be copied as above by a commercially available disk drive, which will be useful for protection of the copyright for the main data in the disk.
On this account, it was proposed to record identification information to the reflective layer of the disk by forming marks which will cause the reflectance of the reflective layer to change. As disclosed in the Japanese Patent No. 3454410, main data such as content data, management information or the like is recorded in the form of a combination of pits and lands to the disk, while sub data as identification information is recorded by forming marks which will make a small change in reflectance of a portion, above the pits or lands, of the reflective layer.
The marks are recorded to the reflective layer of the optical disk by irradiating laser light higher in power than the reading laser light. The change in reflectance caused by the marks is so small that reading of the main data recorded in the form of a combination of pits and lands will not be influenced. Thus, the marks will not be read while the main data is being read.
It should be noted that to read the sub data itself, a separate playing system may be provided to sample many parts of the reading signal of the main data, each given the small change in reflectance, and integrate the samples, for example. In this case, positions where marks are to be inserted as sub data are determined between the sub data recorder and player according to a predetermined algorithm. Thus, in the authenticated disk player, it is possible to identify positions where the marks are to be recorded according to the similar algorithm to a one used for recording and thus read the identification information as the sub data accurately.